[mcguyver]

Stiff selector plate can mean that the plate has started to melt. When you have a high current draw in an AEG with a standard switch, all the current must flow from one of the little "fingers" through the selector plate contact to the other. Often, the lower "finger" is only partially in contact with the selector, and this results in increased resistance at that point, and this translates to heat. I've seen this be so severe that it's actually melted the selector plate, and deforming it. I've also seen it melt the plastic over the contact plate and push the lower "finger" out of the way, breaking contact and making full-auto fire intermittant or impossible.

If you pull the mechbox out and look at that point, you'll see if this is the case.

As for a "burning" junction, it's possible that the excess current draw responsible for the burning did not originate there, unless you have a poor solder joint with a high resistance. The overcurrent situation (ie short circuit) causing the burning could be coming from another spot along any wire in the system, and is only manifesting itself at this point, like if it's got a slightly higher resistance across your splice vs the wire itself. Current follows the path of least resistance, but the flip side of that is the spot with the highest resistance will also be the place where thermal problems manifest themselves. It's the same scenario we look for in contact maintenance for large motor contactors or excessive conductor loading. Heat at a spot does not necessarily mean the problem is right there, but often times it does.

Look over all your wiring. Your problem may actually be at the entrance to the stock tube from the body.